1. Field of the Invention
The present invention relates to a perpendicular magnetic recording head which performs recording by applying a magnetic field onto a recording medium, such as a disk, in a vertical direction. More particularly, the present invention relates to a perpendicular magnetic recording head and a method of manufacturing the same, wherein a magnetization inversion width (a magnetization shift width) among recorded patterns in which magnetization recorded on a recording medium is inversed to one another can be reduced and magnetization inversion noise can be reduced.
2. Description of the Related Art
U.S. Pat. No. 6,501,619 B1 discloses a perpendicular magnetic recording head including a read/write pole serving as a main magnetic pole or a core layer, and a return pole serving as a return yoke layer, wherein a gap layer is formed between the core layer and the return pole, as shown in FIGS. 12 and 16.
In the perpendicular magnetic recording head shown in FIGS. 12 and 16 of U.S. Pat. No. 6,501,619 B1, a recording magnetic field is generated from the read/write pole or the core layer to a data storage layer (that is, a recording medium). The recording magnetic field passes through the data storage layer and then returns to the return pole. If a vertical recording magnetic field is applied from the read/write pole or the core layer, the data storage layer is magnetized in a vertical direction, so that a recording signal is recorded on the data storage layer.
The perpendicular magnetic recording head shown in FIGS. 12 and 16 of U.S. Pat. No. 6,501,619 B1 has a structure in which a surface of the gap layer side of the read/write pole or the core layer is inclined toward the return pole at a predetermined angle with respect to a direction vertical to a top surface of the data storage layer (a surface opposite to the core layer and the return pole).
In the perpendicular magnetic recording head disclosed in U.S. Pat. No. 6,501,619 B1, a recording magnetic field is isotropically spread from the read/write pole or the core layer serving as the main magnetic pole. At this time, as the recording magnetic field becomes wide toward a trailing side or a leading side, the magnetic field strength becomes weak. Upon recording by the perpendicular magnetic recording head, the recording medium moves from the leading side of the perpendicular magnetic recording head to the trailing side. Thus, the recording magnetic field spread toward the trailing side is rewritten on previously recorded patterns (recorded patterns that have been written by a recording magnetic field at the leading side), which have been written on the recording medium. For this reason, the recording magnetic field having the small magnetic field strength, which has been spread on the trailing side, causes a phenomenon that increases a magnetization inversion width (a magnetization shift width) among recorded patterns whose magnetization is inversed to one another. Thus, there is a problem in that magnetization inversion noise caused by the large magnetization inversion width is increased in a reproduction output that is obtained when a reproduction element travels on the recorded patterns. Accordingly, in the perpendicular magnetic recording head, it is necessary to reduce magnetization inversion noise by decreasing the magnetization inversion width.
Such magnetization inversion is generated on the basis of an interface (that is, an isomagnetic interface) where the recording magnetic field strength from the read/write pole or the core layer serving as the main magnetic pole is the same.
The width (an isomagnetic interface width) in a recording medium sliding direction of the isomagnetic interface is related to the magnetization inversion width.
Furthermore, the isomagnetic interface width is related to a magnetic field gradient α of a recording magnetic field. If an absolute value of the recording magnetic field gradient α increases, a magnetization inversion width can be made small. It is thus possible to generate a phenomenon of magnetization inversion noise.
In this case, the relationship between the recording magnetic field gradient a and the magnetization inversion width will be described below. FIG. 2 is a diagram illustrating the relationship between a main magnetic pole and a recording medium of a perpendicular magnetic recording head according to a related art, and a location of the main magnetic pole and a recording magnetic field strength generated from the main magnetic pole.
A reference numeral 130 in FIG. 2 indicates the main magnetic pole of the perpendicular magnetic recording head. Magnetic field strength curves 211 and 212 of FIG. 2 show the relationship between the location using the main magnetic pole 130 as a reference and the magnetic field strength of a recording magnetic field (the recording magnetic field strength) which is generated from the main magnetic pole 130, on a top surface Ma1 and a bottom surface Ma2 of a hard film Ma (that is, a recording layer) of a recording medium M. In FIG. 2, the curve 211 indicates the recording magnetic field strength on the top surface Ma1, and the curve 212 indicates the recording magnetic field strength on the bottom surface Ma2.
As shown in FIG. 2, as it approaches the main magnetic pole 130 (toward a direction Z2 in FIG. 2), the recording magnetic field strength on the top surface Ma1 of the hard film Ma gradually increases. The recording magnetic field strength rapidly increases in a region opposite to a trailing-side cross section 130c in a front-end surface 130a of the main magnetic pole 130.
In the same manner, as it approaches the main magnetic pole 130, the recording magnetic field strength on the bottom surface Ma2 of the hard film Ma gradually increases. The recording magnetic field strength rapidly increases in a region opposite to the trailing-side cross section 130c in the front-end surface 130a of the main magnetic pole 130.
Furthermore, the recording magnetic field strength on the top surface Ma1 of the hard film Ma and the recording magnetic field strength on the bottom surface Ma2 of the hard film Ma have the maximum in a region opposite to the front-end surface 130a of the main magnetic pole 130.
Furthermore, as it becomes spaced apart from the main magnetic pole 130 in the direction Z2, the recording magnetic field strength gradually decreases.
A straight line 250 that overlaps the magnetic field strength curves shown in FIG. 2 refers to the amount of coercive force Hc of the hard film Ma constituting the recording medium M. As shown in FIG. 2, in the perpendicular magnetic recording head H, when the recording magnetic field strength is larger than the coercive force Hc of the hard film Ma (that is, the recording layer), magnetization inversion occurs in the hard film Ma. Thus, the hard film Ma is magnetized in a vertical direction and magnetic data is thus recorded on the hard film Ma.
A magnetization inversion width is a distance W3 from the intersection (c) of the recording magnetic field strength curve 211 on the top surface Ma1 and the straight line 250 indicating the coercive force Hc of the hard film Ma to the intersection (d) of the recording magnetic field strength curve 212 on the bottom surface Ma2 and the straight line 250 indicating the coercive force Hc of the hard film Ma in a direction Z1-Z2 (that is, a recording medium sliding direction), in the recording magnetic field strength curves shown in FIG. 2. Magnetization inversion is generated in the region of the hard film Ma having this distance W3. The distance W3 is the magnetization inversion width W3. The region of the hard film Ma having the distance W3 (that is, a region where magnetization inversion is generated) will be referred to as a region B.
An isomagnetic interface 200 exists within the hard film Ma at a location opposite to the region B where magnetization inversion is generated. Accordingly, a distance (the width of the isomagnetic interface) W4 between a top surface 200a and a bottom surface 200b of the isomagnetic interface 200 in the recording medium sliding direction (the direction Z1-Z2 in FIG. 2) is equal to the magnetization inversion width W3.
In FIG. 2, in the case in which the recording magnetic field of the top surface Ma1 within the magnetization inversion width W3 has a tilt angle θ3 with respect to a virtual vertical line L3-L3 that vertically extends with respect to the top surface Ma1 of the hard film Ma, the magnetization inversion width can be made small by making small the tilt angle θ3. This can result in the phenomenon of magnetization inversion noise. Further, the tilt angle θ3 can be made small by increasing the absolute value of the magnetic field gradient α of the recording magnetic field (the recording magnetic field gradient), which is defined as the recording magnetic field strength in a direction vertical to the top surface Ma1 (a direction Y1-Y2 in FIG. 2) that varies per unit distance of the recording medium sliding direction (direction Z1-Z2 in FIG. 2).
In the perpendicular magnetic recording head disclosed in U.S. Pat. No. 6,501,619 B1, if the recording magnetic field from the read/write pole or the core layer serving as the main magnetic pole is inclined toward the trailing side at a predetermined angle with respect to the direction vertical to the recording surface of the recording medium, the tilt angle θ3 can be made small. Accordingly, the absolute value of the magnetic field gradient α of the recording magnetic field can be increased.
However, FIGS. 12 and 16 of U.S. Pat. No. 6,501,619 B1 do not clearly describe what direction is the trailing side of the perpendicular magnetic recording head. The perpendicular magnetic recording head shown in FIGS. 12 and 16 may not surely make small the magnetization inversion width.
In U.S. Pat. No. 6,501,619 B1, it can be also read that the reason why the surface of the gap layer of the core layer formed in the perpendicular magnetic recording head shown in FIGS. 12 and 16 is inclined is to facilitate film formation.
In FIG. 12 or 16 of U.S. Pat. No. 6,501,619 B1, the surface located at the gap side of the return pole is inclined at a predetermined angle with respect to a direction vertical to the data storage layer, and is thus formed as an inclined surface. In this state, if the gap layer and the read/write pole or the core layer are formed on the inclined surface of the return pole without change, the read/write pole or the core layer can be easily formed. Since the read/write pole or the core layer is laminated on the inclined surface of the return pole, however, the surface located at the gap layer side of the read/write pole or the core layer can be formed to have the same angle as the inclined surface of the return pole. In other words, if the read/write pole or the core layer is laminated on the return pole after the return pole is formed, the read/write pole or the core layer has a shape similar to the shape of the return pole. For this reason, the read/write pole or the core layer is formed to have the tilt angle.
Accordingly, U.S. Pat. No. 6,501,619 B1 never discloses the relationship between a reduction of the tilt angle of the read/write pole or the core layer and a magnetization inversion width or a reduction of magnetization inversion noise. The relationship between them is still unclear.